One of our surveys is made in 2 languages: French and Dutch with the former being the base language.

Dutch-speaking users report the following problem:
* in their invite e-mail they receive the link for the Dutch page (as it should)
* after that first page, any page is in French (the base language)
* if they change language, they can, however sometimes they can't proceed to the next page after filling in the answers, and sometimes the next page is again in French.

It's a bit hard to pinpoint the exact problem, but does anybody have an idea what to go look for?